Bio-chemical researchers involved in high throughput screening and/or drug and chemical development require the capability to characterize millions of samples accurately and rapidly. Due to this requirement, sample testing is often performed in sample plates that may include tens, hundreds, or even thousands of individual sample wells. The use of such multi-well sample plates simplifies automation of sample testing, assuming the necessary test equipment is compatible with multi-well sample plates.
In designing high throughput test apparatus, typically a variety of system constraints are considered. The first critical design parameter is the intended use of the test apparatus. For example, the apparatus may be designed to characterize a sample's absorption, luminescence, or fluorescence properties. Additionally, the test apparatus may be designed to be capable of testing more than one property. A second critical design parameter is the size and format of the sample plate. Currently there are a variety of available standard format sample plates containing varying numbers of sample wells and types. These sample plates typically have different external dimensions and may also have different sample well dimensions. Although most instruments are designed to handle only a specific sample plate format, some instruments are designed to handle a range of sample plate formats. A third design parameter that is typically taken into account is the size and design of the individual sample wells. For example, sample wells vary in size from microns in diameter as utilized in some chip sample plates to millimeter sized wells or larger. Additionally, sample wells may be of varying depth, comprised of transparent or opaque materials, and utilize any of a variety of shapes, e.g., square or round cross-sections. Sample wells may also include a reflective bottom surface. Preferably an instrument is capable of handling a range of sample well types.
In a standard multi-well sample plate testing apparatus the sample plate is held within a holding fixture that is coupled to one or more scanning mechanisms. The scanning mechanisms allow the sample plate to be moved along at least one axis relative to the portion of the instrument used to characterize the sample (e.g., an excitation source and a fluorescence detector). Preferably the scanning mechanisms allow the sample plate to be moved along two axes, thus allowing a two-dimensional array of sample wells to be analyzed. Although moving the sample plate may cause problems such as sample spillage, typically these problems are minor in comparison to the difficulties associated with scanning the test head relative to a fixed sample plate. For example, to avoid sample spillage during plate movement, the plate can be moved at a slower rate and utilize gradual start and stop cycles. Additionally, the level of liquid within each sample well can simply be sufficiently below the top of the sample well to avoid spillage.
An instrument that provides the benefits of multi-well sample plate scanning without the drawbacks associated with translating the sample plate along multiple axes is desired. The present invention provides such an instrument.